Kirkwood gaps

Kirkwood gaps, interruptions that appear in the distribution of asteroid semimajor axes where the orbital period of any small body present would be a simple fraction of that of Jupiter. Several zones of low density in the minor-planet population were noticed about 1860 by Daniel Kirkwood, an American mathematician and astronomer, who explained the gaps as resulting from perturbations by Jupiter. An object that revolved around the Sun in one of the gaps would be disturbed regularly by Jupiter’s gravitational pull and eventually moved to another orbit. Some of those gaps are the primary sources of the near-Earth asteroids, which form from collisions between main-belt asteroids located close to a Kirkwood gap. Those collisions produce small asteroids that then have their orbits perturbed by the Yarkovsky effect (a small force that is due to the anisotropic emission of thermal radiation from an asteroid’s surface and works most efficiently on small asteroids), allowing them to drift into the Kirkwood gap. By the same Jupiter perturbations that originally cleared those gaps, those small asteroids evolve into orbits that cross Earth’s and from which they are eventually ejected from the solar system unless they first collide with a planet.

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any of a host of small bodies, about 1,000 km (600 miles) or less in diameter, that orbit the Sun primarily between the orbits of Mars and Jupiter in a nearly flat ring called the asteroid belt. It is because of their small size and large numbers relative to the major planets that asteroids are...

any natural solar system object other than the Sun and the major planets and dwarf planets and their satellites (moons). The small bodies populate the solar system in vast numbers and include the mostly rocky asteroids, or minor planets, the predominantly icy comets, and the fragments of such...

the most massive planet of the solar system and the fifth in distance from the Sun. It is one of the brightest objects in the night sky; only the Moon, Venus, and sometimes Mars are more brilliant. Jupiter is designated by the symbol ♃.